The goal of this research is to develop a clearer understanding of the impact on youth of changes in state laws regarding the use of possession of marijuana. Using national data from the high school and a longitudinal panel from the class of 1975, we will make before and after comparisons of illicit drug use, alcohol use, etc., contrasting seven states in which the laws were recently liberalized with other states in which they were not. Supplementary samples were added to the national Monitoring the Future project samples in the seven states undergoing decriminalization. All field and measurement procedures were identical to the parent project.